Prof. Woodie Flowers takes a hard line against MITx in its current form arguing (among other things) that (a) "education" is not the same as "training", and that (b) online resources are probably good for "training":

I believe that education and training are different. To me, training is an essential commodity that will certainly be outsourced to digital systems and be dramatically improved in the process. Education is much more subtle and complex and is likely to be accomplished through mentorship or apprentice-like interactions between a learner and an expert. [...]

Education is the source of comparative advantage for students. Education is worth its cost. Person-to-person training often is not worth its cost.

To clarify a bit: Learning a CAD program is training while learning to design requires education; learning spelling and grammar is training while learning to communicate requires education; learning calculus is training while learning to think using calculus requires education. In many cases, learning the parts is training while understanding and being creative about the whole requires education.

We seem to have decided to offer “courses” rather than participate in the exciting new process of replacing textbooks with more effective training tools.

Apple just announced their software system to support new-media texts. If they do for textbooks what iTunes did for music distribution, the tipping point will be passed.

All early indicators are that E. O. Wilson’s Life on Earth is the current gold standard for digital biology texts. The first two chapters are already offered through Apple’s new e-text system. These chapters are impressive. The entire text will require years of work by a talented team and already represents an investment of millions.

These are early days for online (or, more broadly, web-enabled) education, so it's not clear what may work well, what may not, and how much of the success/failure can be attributed to the use of the web. It will probably take a few years before these issues are settled with some (semi)definitive evidence. In the meantime, it's time for experiments, lots and lots of them.

I think we already have some evidence that short video explanations of concepts / phenomena / examples, à la Sal Khan, work well. Hour-long video lectures? Not much, unless they are delivered by rock-star teachers. As the experiments progress, we will get a clearer picture of the kinds of things that work well online. The IHE story also touches on this experimental nature of MITx:

The goal of developing virtual laboratories and software that automatically assesses students’ ability to vanquish complex problems and tasks is not to eliminate the need for real, live professors, says Sussman; it is to figure out what parts of the face-to-face delivery model can be automated so professors and students can double-down on the pieces of an MIT education that are oriented to apprenticeship.

MITx may have the official backing of its parent institution, and others, like Udacity and Coursera, may have the "brand pull" of some of their charismatic founder-teachers. [And a company called 2tor seems to be making waves, too, with its "expensive" model.] But these are all just early experiments -- online education is yet to get out of its Friendster days.